1. Technical Field
The present invention relates to a polymer membrane having a covalent network structure and a method for producing the same. More particularly, the present invention relates to a porous polymer membrane including porous organic framework nanoparticles and a polymer matrix, and a method for producing the porous polymer membrane.
2. Description of the Related Art
Porous membranes as membranes for use in membrane separation processes can be broadly classified into symmetric membranes whose cross section has a uniform structure as a whole, and asymmetric membranes consisting of a thin active layer having fine pores and a support layer having larger pores. Such an asymmetric membrane can be produced by a phase inversion method using a homogeneous single-phase polymer solution and has the advantage of high permeability due to the introduction of the thin active layer.
When it is intended to produce a membrane suitable for an intended application by a phase inversion method, removal of a solvent, addition of a non-solvent and temperature regulation should be accurately conducted during phase inversion, causing inconvenience in precisely controlling various processing conditions, including humidity, evaporation rate of the solvent, kind of the non-solvent and drying conditions. Further, the phase inversion brings about considerably low mechanical strength and poor chemical stability of the polymer membrane. Since an active layer and a support layer of the membrane are simultaneously formed using a homogeneous polymer solution, there exists a practical limitation in improving the permeation performance of the polymer membrane.
Under these circumstances, research has been conducted on composite membranes in which an active layer is formed on a porous support layer made of different materials by interfacial polymerization, and nanocomposite membranes into which porous nanoparticles are introduced to achieve improved permeation performance.
Examples of porous materials suitable for use in the nanocomposite membranes into which porous nanoparticles are introduced include metal-organic frameworks (MOFs). A group led by Omar Yaghi, U.S.A. has conducted pioneer research on microporous coordination polymers of MOFs in which metal ions are three-dimensionally connected to a hydrocarbon organic compound to form micropores. During synthesis, carboxylic acids at both ends of the organic compound exist as anions and are coordinated to the metal cations. That is, the organic compound acts as a ligand connecting both metal ions. However, a MOF composed of a ligand, such as 1,4-benzene dicarboxylic acid, and a transition metal (Zn4O) cluster, which was proposed by the Yaghi's group, has a large specific surface area but is known to be susceptible to moisture upon exposure to air. A group led by Ferey, France, has presented a MOF material in which 1,3,5-benzene tricarboxylic acid as a ligand is bonded to Cr metal ions. This MOF material also has a large specific surface area but has poor resistance to temperature, which limits its use in various applications.